Evidence for an ordered Pd 7Gd phase in PdGd alloys

Abstract

The PdGd alloys in the composition range 8.0–21.0 at.% Gd were studied by X-ray diffraction, electron microscopic observations, electrical resistance measurements and metallographic examinations. The results for annealed alloys (with the exception of the 21.0 at.% Gd alloy) indicate the presence of long-range order in the form of a Pd 7Gd superlattice. This is similar to the order found in Pd 7Ce and Pd 7Y, which are isomorphous with Pt 7Cu. The order-disorder transition of the ordered Pd 7Gd phase in the Pd-Gd alloys in the composition range 11.5–17.5 at.% Gd is accompanied by the peritectoid reaction, Pd 7 Gd  α- Pd + L1 2-type Pd 3 Gd, at T c = 810 ± 10 K. Evidence was found for the existence of the same ordered phase in the Pd-8.0at.%Gd and Pd-10.0at.%Gd alloys from electron diffraction and electrical resistance measurements. The palladium-rich portion of the phase diagram of the PdGd system is presented in a revised form taking into account the ordered Pd 7Gd phase.